Field
This disclosure relates generally to electronic circuits and more specifically to an analog delay cell and tapped delay line using the analog delay cell.
Related Art
FIG. 1 illustrates a conventional feed-forward equalizer 10 having a pre-filter 12, tapped delay line 14, and decision feedback equalizer (DFE) and finite impulse response (FIR) block 20. In one embodiment, pre-filter 12 is a continuous-time linear equalizer (CTLE). Tapped delay line 14 includes a plurality of delay cells, or elements, 16, a plurality of multipliers 18, and a summation circuit 38. The plurality of delay cells 16 includes a plurality of representative delay cells 22, 24, and 26 connected together in series. The plurality of multipliers 18 includes multipliers 28, 30, 32, 34, and 36. An input of each of the multipliers 18 is connected to an output of each of the delay elements 16, and an output of each of the multipliers is connected to an input of the summation circuit 38.
The plurality of delay cells 16 may be implemented in a number of ways. One way to implement delay in a tapped delay line uses transmission lines, or artificial transmission lines (with a lump LC network). However, the transmission lines may require long lines and large dimension components to implement. Also, the resulting bandwidth may be too narrow and need many segments for high speed SerDes (serializer/deserializer) applications. Conventional active analog delay cells with active inductors may require further inductance compensation circuits, and it may be difficult to maintain the consistency of the delay lines. In addition, an active inductor may have its own bandwidth limitations. Prior digital-based delay cells, for example, D-type flip-flops, or latches, may not be able to support the required high speed capacity at data rates greater than about 10 gigabits per second (Gb/s). Also, digital-based delay cells may not be able to support small input data amplitudes due to intersymbol interference (ISI).
Therefore, what is needed is an analog delay cell that solves at least some of the above problems.